Lecture 3aNaming Soil Horizons

Soil horizons (layers in the soil) are named so differences between soils can be identified.

Naming soil horizons takes practice

When soil scientists are describing a soil they will discuss a lot about what they are seeing and how it should be named.

And what they are not seeing and what it should not be called ?

Soil Judging Students wanting more practice at naming soil horizons should

take Soil 4511 and try out for the Soil Judging Team Students that participate in the “Soil Judging” contest get more practice with different soils from the region. (MN, SD, ND,MO,IA,KS,NE.

The contest this fall is in Minnesota near Cloquet.

Contest in Kansas 2006

2007 UM Soils Team in the Team Pit No. 1 in southwest Iowa: Left to right Meryl Larson, Erin Andrews, Nick Reep, and Nick Saumweber

Organic Horizons O - horizon - organic

material (no mineral materials) 1) forest litter 2) organic soil or peat soils, or muck

Oi - undecomposed (fibris) Oe - moderate decomp.

(hemis) Oa - decomposed (sapric)

Organic Soil Profile

This trenchingmachine is diggingthrough the Oe horizon of an organic soil.

Trenches needed to remove water so thepeat will dry beforeharvest.

Organic Soil Horizons in a forest litter

Oi

Oe

Processes of Mineral Soil Horizon Formation

A. Additions - H2O, organic matter,air, soil particles, salt

B. Losses - H2O, organic matter, CO2 , nutrients by plant removal

C. Transformations - Changes to soil structure, development of clay minerals, weathering of minerals to elements, chemical Rx

D. Translocations - movement from one horizon to another of O.M. Clay, Water, Iron, & Nutrients in colloidal size, (very small particles) clay films on peds are evidence of this translocation = clay (film) coating

Mineral Soil Horizons

A horizon - surface horizons that accumulate O.M.

Ap = plowed soil

Ap

EB

Bt

BC

C

Ap

E Horizons

E - (formerly A2) - Translocation out - Zone of Eluviations - Leaching out

lighter in color than horizons above or below

AE

E/B

Bt

BCC

B Horizons- two kinds:

a) Translocation in - below an A, E, or O with an accumulation of clay, iron, humus (O.M. decomposed.) or carbonates (CaCO3) zones of illuviation

b) or alteration of the original parent material, development of color or structure - Bw

Bt

C Horizons C - little affected by

pedogenic processes and lack properties of O-A-B-E- or is the Parent Material

C horizon

Solum = A + B

Rock Horizons R = hard rock Cr = Soft

Rock

Subscripts - all B horizons have a subscript, most

transition horizons do not.

* a - sapric - organic soils - well decomposed * b - buried soil horizon d - dense - geogenic soil material (compacted by

glacier) * e - hemic - mod. decomp. - organic soil f - frozen soil - permanently frozen, permafrost * g - gleyed soil - gray color due to low O2 - reduction of

Fe * h - accumulation of humus - O.M. other than in the A or

O horizons * i - fibric - organic - non-decomposed * k - accumulation of calcium carbonate (CaCO3) * m - cementation - hard - indurated

n - sodium accumulation * p - plowing - only used with A q - silica accumulation - very weathered or old soil * r - soft rock - used with C or Cr * s - sesquioxides (1.502) (Fe2O3) accumulation of Fe

and Al - red color *ss – slickensides present –shiny surface on ped face

caused from soil rubbing against soil * t - clay accumulation - clay films * w - color or structure development (Bw) x - Fragipan - hard, dense layer that developed with

time y - gypsum accumulation (CaSO4) z - salts more soluble than gypsum

(KCL - NaCl - NaSO4)

Subscripts cont.

Transition Horizons

AB - Like A - some of B BA - Like B - some of A AE AC BC

E/B - Both E and B particles

are present - “B & E” used for soils

with Lamellae - thin bands of accumulating clay and iron in sandy soils

Lithologic Discontinuity A1 A2 2B Designated by number in

front of horizon. (More than one

parent material)2 parent

materials

Practice at naming horizons – Soil from Badlands of North Dakota---Texture of horizons 1,2,3,4 = loam---Note Carbonates in horizon 3

---

A --- AB --- Bk --- C

DYAD – Name 4 horizons Using one transition horizon

Sandy soil from Northeast MinnesotaTexture of Horizon 1,2,3,4 = Sand

Goodhue County Soil, Southwest of Redwing Mn.Texture of horizon 1 & 2 = Silt Loam, Hrz 5 = Silty ClayHrz. 4 = Cobbly loam, Hrz. 5 = Loam

A E Bt 2BC 2C